Method of simultaneously forming a plurality of filaments



CCL 11, 1956 H. H. WEBBER ETAL 3,277,564

METHOD OF SIMULTANEOUSLY FORMING A PLURALITY OF FILAMENTS Original Filed March 14, 1963 F151 F152 F155 FELL United States Patent() 3,277,564 METHOD F SIMULTANEOUSLY FORMING A PLURALITY OF FILAMENTS Harold H. Webber, Groton, Mass., and Albert H. Wilson, Jr., De Land, Fla., assignors to Roehr Products Co., Inc., a corporation of Delaware Continuation of application Ser. No. 265,262, Mar. 14, 1963. This application June 14, 1965, Ser. No. 463,759 19 Claims. (Cl. 29-419) This application comprises a continuation of our c0- pending application Serial No. 265,262, filed March 14, 1963, now abandoned.

This invention relates to the forming of filaments and in particular to the simultaneous forming of a plurality of fine filaments having a diameter of approximately 10 microns or below.

There has long been a need for high lstrength metallic filaments and the like for use in fabrics having improved physical characteristics as compared to the conventional textile fabrics such as cotton, wool and the like. One example of such a need is that of the automotive vehicle tire industry wherein reinforcing fabrics of many different types have been employed over the years in an attempt to find a completely satisfactory carcass reinforcing fabric.

Further, recent investigations of the tensile strength of small diameter metal filaments such as whiskers of iron, copper, silver and the like having a diameter of under l microns have indicated that filaments of this type having a diameter of approximately 4 microns or less have increased tensile strength substantially beyond the expected tensile strength as determined by Hookes law. Thus the desirability of forming such small diameter filaments in substantial quantities and at relatively low cost is manifest. The present invention comprehends an improved process for producing such filaments at such low cost and thus makes available for the first time comercially practical high strength filaments of metal and the like for use in improved fabrics, cables, filter media, superconductive bodies, etc.

Thus a principal feature of the present invention is the provision of a new and improved method of forming filaments.

Another feature of the invention is the provision of such a method of forming filaments at low cost.

A further feature of the invention is the provision of such method adapted to provide such filaments having a diameter of approximately microns and below and in substantial lengths such as approximately 50 feet and over.

Still another feature of the invention is the provision of such method of forming filaments providing controlled uniformity and non-uniformity of the filament diameter as desired.

Yet another feature of the invention is the method of forming laments providing unburnished metal yarn wherein the filament bundles may have a preselected twist for improved torque and balance characteristics.

A further feature of the invention is the provision of such a method adapted to provide filaments having controlled resistivity.

Still another feature of the invention is the provision of method of forming filaments including the steps of sheathing each of a plurality of elongated elements from which the filaments are to be formed with a material having physical characteristics differing from those of the elements when desired, bundling the sheathed elements in substantially parallel relationship, drawing the bundle to reduce the cros-s-section Iof the elements therein to a preselected lament cross-se-ction, and removing the sheathing material.

Other features and advantages of the invention will be :apparent from the following description taken in connection with the accompanying drawing:

FIG. 1 is a transverse cross-section of a metal wire from which a filament may be formed in accordance with the invention;

FIG. 2 is a transverse cross-section of the wire disposed within a coaxial sheath as in a first step of the method embodying the invention;

FIG. 3 is a transverse cross-section of the wire and sheath assembly with the sheath reduced in diameter as in a subsequent step;

FIG. 4 is a transverse cross-section of the sheathed wire structure as reduced in diameter in a further subsequent step;

FIG. 5 is a transverse cross-section of a plurality of sheathed Wire structures of FIG. 4 arranged within a further sheath to define 4a bundle;

FIG. 6 is a transverse cross-section of the bundle of FIG. 5 as reduced in diameter in a subsequent step;

FIG. 7 is a transverse cross-section of a plurality of the reduced-diameter bundles of FIG. 6 disposed in a further sheath to define a bundle of said bundles;

FIG. 8 is a transverse cross-section of the bundle of FIG. 7 as reduced in diameter in a subsequent step;

FIG. 9 is a transverse cross-section of a plurality of the reduceddameter bundles of FIG. 8 disposed in a further sheath to define a bundle. of said bundles;

FIG. 10 is a transverse cross-section of the bundle of FIG. 9 reduced in diameter in a subsequent step;

FIG. 1l is a fragmentary diagrammatic vertical section of an apparatus for drawing the fila-ments in practicing the method embodying the invention;

FIG. 12 is a vertical cross-section of a tank wherein the reduced diameter bundle of FIG. 10 is disposed to be acted upon by a suitable fluid within the tank to remove the sheath material from the bundle; and

FIG. 13 is a tow of filaments embodying the invention.

In the exemplary embodiment of the invention as disclosed in the drawing, a tow generally designated 10 of filaments 11 is formed by a process wherein a plurality of relatively large diameter wires 13 are constricted or otherwise reduced in diameter in a bundle arrangement so as to result in the individual filaments 11 being of extremely small diameter while yet of substantial length. More specifically, the invention comprehends the forming of metal filaments and the like having a diameter of approximately 10 microns more or less and down to under 1 micron if desired. Thus the invention may be employed in the formation of fine filaments including Whisker-type filaments where-in substantially single crystal diameters are provided. Further, the invention comprehends the provision of such fine filaments in Vsubstantial lengths such as approximately 50 feet and over whereas heretofore whiskers have been limited to relatively short lengths due to the presence of fracture points and the like occurring .in the known methods of formation thereof.

The present invention comprehends the forming of such fine filaments by constriction of a plurality lof wires and more specifically by successive drawing operations. In the illustrated embodiment a wire 13 having a relatively large diameter such as over .05 inch is firstly encased in a sheath 14 of suitable matrix material. As shown in FIG. 2, the sheath may have an internal diameter slightly larger than the external diameter of the wire 13 to permit facilitated coaxial assembly thereof. As indicated briefly above, the filaments 11 may comprise metal filaments. Examples of material of which the wire 13, and thus the filaments 11 may be formed by the present process, comprise niobium, stainless steel, nickel, tungsten, iron, aluminum, carbon steel, and chrome nickel alloys, land other suitable drawable materials The wire 13 may be suitably formed to have an originally small diameter by any suitable method including melt forming, foil slitting, electrodeposition, vapor phase deposition, chemical deposition, powder forging, and `suitable conventional wire forming processes. It is preferable that the wire 13 be relatively free of occlusions and the like to preclude formation of fracture points in the wire in the drawing process. The wire may have any suitable cross-section including the circular cross-section illustrated in FIG. 1. Further, lthe wire may be longitudinally uniform in cross-section or may vary as desired.

The sheath 14 may be formed of a suitable matrix material which will act generally as a fluid medium under the pressures induced at the locality of the drawing dies. Examples of such matrix material are metals such as copper and iron.

As shown in FIG. 3, the sheath 14 is firstly constricted onto the wire 13 to lmake a tight physical bond between the sheath and the wire so that in subsequent drawing steps the sheath 14 remains fixed relative to the wire 13 and does not stretch thereover. The assembly 15 of the wire 13 and thusly reduced sheath 14 is next drawn down through a suitable die such as die 16 illustrated in FIG. l1. The assembly 15 is forced through the die by suitable pulling means diagrammatically illustrated at 17 in FIG. 11. The resultant reduced-diameter sheathed wire generally designated 13 is illustrated in FIG. 4.

A plurality of sheathed wires 1S are next disposed within a sheath 19 formed of a suitable matrix material which may, but need not necessarily, comprise the same material as sheath 14. As shown in FIG. 5, the sheathed wires 18 may be uniformly distributed Within the sheath 19 where it is desired to obtain filaments 11 of generally uniform cross-section.

The bundle 20 of sheathed wires 18 in sheath 19 is then drawn down to define a reduced diameter bundle generally designated 21 as shown in FIG. 6. The plurality of the reduced diameter bundles 21 may then be disposed within a further sheath 22 as shown in FIG. 7 to define a further bundle generally designated 23. The bundle 23 may then be drawn down to define `a reduced diameter bundle generally designated 24 as shown in FIG 8. A plurality of the reduced diameter bundles 24 may then be disposed within a further sheath 25 as shown in FIG. 9 to define a further bundle lgenerally designated 26. The bundle 26 may then be drawn down, as shown in FIG. 10, to define a final reduced-diameter bundle generally designated 27.

The number of wires and bundles disposed within the bundling sheaths and the number of drawing steps may be varied as desired to obtain the desired resultant filament diameter; for facilitated illustration of invention we have shown three bundling and subsequent drawing steps with seven sheathed wires and bundles being disposed within the respective bundling sheaths, it being understood that more or less wires, bundles, and steps may be employed as desired.

The individual filaments 11 are obtained from the final bundle 27 by removing the matrix material which comprises the various sheaths employed in the drawing operation. As illustrated in the drawing, the respective constricting operations effected by the drawing steps cause the sheath material to substantially completely fill the voids between the wires so as to form a matrix extending substantially continuously in cross-section whereby each of the wires in the respective bundles is rmly `and positively supported by the matrix material during the drawing thereof through the drawing die 16. As indicated briefiy above, the matrix material preferably comprises a material capable of acting in the manner of a fluid under the pressure induced at the drawing die so as to provide improved support of the wires during the drawing operation and thereby effectively preclude the formation of discontinuities in the respective wires.

The respective filaments 11 are subsequently made to comprise a filament tow by the removal of the matrix material in a subsequent step of the forming process. The present invention comprehends the removal of the matrix material by suitably acting on the final bundle 27 to eliminate the matrix material while allowing the filaments to remain. Thus the invention comprehends the use of a matrix material which differs in physical characteristics from the wire material from which the filaments are formed (eg. the matrix and wire material may differ chemically) in such a manner as to permit the ready removal of the matrix material without substantially affecting the laments. For this purpose, the sheath-matrix material may comprise, as indicated above, copper where the fifament material is stainless steel permitting the copper to be removed by treatment with suitable copper-dissolving acid, such as nitric acid, which leaves the stainless steel filaments substantially unaffected. Other methods of rcmoval of the matrix may be employed with suitable matrix materials permitting the removal thereof such as by electrolysis, shock, melting, physical break-up as by chop ping and the like.

In the illustrative example of matrix removal step, as shown in FIG. 12, the bundle 27 is disposed in a suitable tank 2S containing a body 29 of solubilizing fluid such as nitric acid, the matrix material of `bundle 27 illustrated therein being copper and the filaments being stainless steel. Thus upon complete removal ofthe copper matrix material the individual filaments 11 define a tow 10 of stainless steel filaments as shown in FIG. 13, each lilament being separate of the other filaments and of preselected small diameter.

Specific examples of filament forming processes cmbodying the invention are as follows:

Example 1.-A Wire 13 of type 302 hard drawn stainless steel having a diameter of .081 inch is inserted into a copper tube sheath 14 having a .125 inch outer diam eter and a wall thickness of .020 inch. In the first step thc sheath is drawn down to an outer diameter of .109 inch. The resultant sheathed wire 1S is then annealed at a temperature of approximately l800 F. The reduced sheathed wire 18 is then subsequently drawn seriatim in a number of similar drawing and annealing steps until the final outer diameter of the sheath wire 18 is approximately .016 inch.

The .016 inch diameter sheathed wire 18 is then cut into 19 pieces and inserted into a copper sheath 19 having an outer diameter of approximately .125 inch and a wall thickness of approximately .O15 inch. The sheath is then drawn down to an outer diameter of .109 inch and the assembly annealed at approximately 1800D F. The resultant bundle 20 is then drawn down in successive steps including interposed annealing steps to an ultimate diameter of .016 inch. The resultant reduced diameter `bundle 24 is then cut into 19 pieces and inserted in a copper sheath 26 similar to sheath 19. The above steps are then repeated to again reduce the bundle to final diameter of .O40 inch wherein the individual wires have `been reduced in diameter to define filaments having a diameter of `approximately .0005 inch. Alternatively the final draw may be to a diameter of .032 inch to produce filaments of approximately .0004 inch diameter, or to a diameter of .028 inch to produce filaments of approximately .00032 inch diameter. The matrix copper material is then dissolved in tank 28 with the nitric acid 29 being maintained at a temperature of approximately F.

Example 2.A stainless steel wire 13 having a diameter of .083 inch is inserted into a copper tube sheath 14 having a .125 outer diameter and a wall thickness of .020 inch. In the first step the sheath is drawn down to an outer diameter of .109 inch. The resultant sheathed wire 18 is then annealed at a temperature of approximately 1800 F. The reduced sheathed wire 18 is then subsequently drawn seriatim in a number of similar drawing and annealing steps until the final outer diameter of the sheathed wire 18 is approximately .016 inch.

The .016 inch diameter sheathed wire 18 is then cut into 7 pieces and inserted into a copper sheath 19 having an outer -diameter of approximately .072 inch and a wall thickness of approximately .009 inch. The sheath is then drawn down to an outer diameter of .065 inch and the assembly is .annealed at approximately 1800 F. The resultant bundle is then drawn down in successive steps, including interposed yannealing steps, to an ultimate diameter of .016 inch. The resultant reduced diameter bundle 24 is then cut into 7 pieces and inserted in a suitable copper sheath 26 similar to sheath 19. The above steps are then repeated to reduce the bundle to a final diameter of .016 inch wherein the individaul wires have been reduced in diameter to define filaments having :a diameter of approximately .00032 inch. Alternatively, the final draw may be to a diameter of .032 inch to produce filaments of approximately .0047 inch diameter, or to a diameter of .025 inch to produce filaments of approximately .0004 inch diameter. The matrix copper material is then dissolved in tank 28 with the nitric acid 29 being maintained at a temperature of approximately 120 F.

Example .S2-A wire 13 of type 302 hard drawn stainless steel wire having a diameter of .083 inch is inserted into a copper tube sheath 14 having a .125 inch outer diameter and a wall thickness of .020 inch. ln the first step the sheath is drawn down to an outer diameter of .109 inch. The resultant sheathed wire 18 is then annealed at a temperature of approximately 1800 F. The reduced sheathed wire 18 is then subsequently drawn seriatim' in a number of similar drawing and annealing steps until the final outer diameter of the sheathed wire 18 is approximately .025 inch.

The .025 inch diameter sheathed wire 18 is then cut into 37 pieces and inserted into a copper sheath 19 having an outer diameter of approximately .250 inch and a wall thickness of approximately .030 inch. The sheath is then drawn down to an outer diameter of .225 inch and the assembly is Iannealed at approximately 1800 F. The resultant bundle 20 is then drawn down in successive steps, including interposed annealing steps, to an ultimate diameter of .025 inch. The resultant reduced diameter bundle 24 is then cut into 37 pieces and inserted in a suitable copper sheath 26 similar to sheath 19. The above steps are then repeated to reduce the bundle to a final diameter of .049 inch wherein the individual wires have been reduced in diameter to define filaments having a diameter of approximately .0005 inch. Alternatively, the final draw may be to a diameter of .035 inch to produce filaments of approximately .0004 inch diameter, or to a diameter of .028 inch to produce filaments of approximately .0003 inch diameter. The matrix copper material is then dissolved in tank 28 with the nitric acid 29 being maintained at a temperature of approximately 120 F.

Example 4.-A wire 13 of alloy 270 soft nickel having a diameter of .063 'inch is inserted into a copper tube sheath 14 having a .095 inch outer diameter and a wall thickness of .015 inch. The sheathed wire is drawn seriatim in a number of drawing and annealing steps until the final outer diameter of the sheathed wire 18 is approximately .016 inch.

The .016 inch diameter sheathed wire is then cut into 19 pieces and inserted into a copper sheath 19 having an outer diameter of approximately .125 inch and a wall thickness of approximately .015 inch. The bundle 20 is drawn down in successive steps to an ultimate diameter of .018 inch. The reduced diameter bundle is then cut into 19 pieces and inserted in a suitable copper sheath 26 similar to sheath 19. The above steps are then repeated to again reduce the bundle to a final diameter of .028 inch wherein the individual wires have been reduced in diameter to define filaments having a diameter of approximately .0004 inch. The matrix copper material is then dissolved in tank 28 with the nitric acid 29 being maintained at a temperature of approximately 120 F.

Example 5.-A wire type of 304 'hard drawn stainless steel having a diameter of .062 inch is inserted into a copper tube shea-th 14 having a .095 inch outer diameter and a wall thickness of .015 inch.v The sheathed wire `18 is then subsequently drawn seriatim in a number of similar drawing and annealing steps until the final outer diameter of the sheathed wire -18 is approximately .016 inch.

The .016 inch diameter sheathed wire 18 is then cut into 19 pieces and inserted into a copper sheath l19 having an outer diameter of approximately .125 inch and a wall thickness of approximately .15 inch. The sheath is then drawn down to an outer `diameter of .109 inch and the assembly is annealed at approximately 1800 F. The resultant bundle 20 is then drawn down in successive steps, including interposed annealing steps, to an ultimate diameter of .016 inch. The resultant reduced diameter bundle 24 i-s then cut int-o 19 pieces 'and inserted in a suitable copper sheath 26 similar to sheath 419. The above steps are then repeated to reduce the bundle to a diameter of .028 inch. The reduced bundle is then cut into 7 pieces and inserted into ya copper sheath having an outer di-ameter of .125 inch `and a wall thickness of *.015 inch. The bundle is then drawn down by successive steps to a diameter of .0l-6 inch. This reduced diameter bundle is then cut into 19 pieces and inserted int-o a copper sheath having an outer diameter of .i inch and ya wall thickness of .015 inch. This bundle is then drawn down by successive steps to `a final diameter of .032 inch wherein the filaments 11 have a -diameter of approximately .00010 to .00012 inches.

Example 6.-A wire 13 4of type 304 stainless steel having a diameter of .062 inch is inserted into -a low carbon steel tubular sheath 14 having an outer diameter of .125 inch and a wall thickness of .023 inch. The sheathed wire is drawn seriatim in a number `of drawing and annealing steps until the final outer diameter thereof is approximately .020 inch. f

The .020 inch sheathed wire 18 is then cut into 19 pieces 'and inserted into a llow carbon steel sheath. 19 ha'ving an outer diameter of approximately 1.56 inches and a wall thickness of approximately .023 inch. The bundle 20 is drawn down in successive steps to an ultimate diameter of .020 inch. The reduced diameter bundle is then cut into 19 pieces and inserted into -a cop-per sheath 26 similar t-o she-ath 19. The above steps are then repeated to lreduce the bundle to a final diameter of .025 inch wherein the individual filaments have a diameter of approximately .0004 inch.

The resultant Ifilaments 11 by virtue of their extremely small diameters have textile characteristics in that they are highly compliant (i.e. they will bend around their own diameter without a permanent set), are fiexible, `and may be used in conventional textile machinery for forming fabrics and the like. The filaments may be formed in substantial lengths such as over 50 feet. Such continuous filaments are highly desirable in fabric formation as compared to the short stable fibers obtainable in other filament forming processes such as cold .and hot drawing, cold yand hot swaging, cold and hot rolling and cold and hot extrusion processes. l

The t-ows 10 may be provided with the individual filaments 1-1 therein having a preselected twist by suitably twisting the bundles during the drawing steps. By suitably lannealing the twisted drawing bundle, the twisted arrangement of the filament may be permanently set therein. Thus, by suitably twisting the individual bundles of the multiple bundles 23 and 26 substantially complete elimination of twisting forces in the composite multiple bundle may be obtained. Still further, by p-rovid-ing the wires 13 with varying diameter in the longitudinal direction, the resultant iilaments may correspondingly have varying diameters along their longitudinal extent `as desired. As the resistivity of the wires is a function of the cross-section diameter of the wires controlled resistivity may be obtained.

While we have shown and described embodiments of our invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction arld arrangement may be made without departing from the spirit and scope of the invention as defined in the `appended claims.

We claim: 1. The method of forming a tow of substantially bare filaments comprising the steps of:

sheathing each of a plurality of elongated drawable rnetal elements from which the filaments are to be formed with a tubular sheath fo-rmed of ta material having characteristics permitting the shea-ths to be pressed together to form la substantially monolithic ybody and differing chemically substantially from :those of the elements to permit separation of the sheath material from elements when desired;

bundling the sheathed elements in substantially parallel relationship; mechanically working the bundled sheathed elements in at least one working step to reduce the cross-section of the elements to a preselected filament crosssection of less than approximately 10 microns maximum transverse dimension and to cause the sheath material to form a matrix extending substantially continuously lin cross-section thereby to preclude separation of individual sheathed filaments; and

substantially completely removing the sheathing material while maintaining the filaments in bundled relationship to provide a tow of substantially bare separate filaments.

2. The method of forming a tow of substantially bare filaments comprising the steps of:

sheathing each of a plurality of elongated elements from which the filaments are to be formed with a material having characteristics differing chemically substantially from those of the elements to permit `separation of the sheath material from the elements when desired;

bundling the sheathed elements in substantially parallel relationship;

`drawing the bundle to reduce the c-ross-section of the elements -therein to a preselected filament cross-section;

bundling a plurality of the drawn bundles in substantially parallel relationship;

drawing the -bundle iof bundles to further reduce the cross-section of the elements therein to a preselected filament fin-al cross-section; and

substantially completely removing the sheathing material.

3. The method of claim 2 wherein the bundles a-re drawn to a final outer diameter substantially equal to the final outer diameter of the sheathed elements as obtained in the element sheathing step.

4. The method of claim 3 wherein the drawn bundles are cut and the cut portions `are disposed in side-by-side relationship in the step of bundling the drawn bundles.

5. The method of claim 3 wherein the sheathed elements are cut and the cut portions are disposed in sideby-side relationship in the step of bundling the sheathed elements.

6. The method of claim 3 wherein the bundle of bundles is disposed within another sheath prior to the drawing thereof.

7. The method of forming a tow of substantially bare filaments comprising the steps of:

sheathing each of a plurality of elongated elements from which the filaments are to be formed with a tubular sheath formed of a material having characteristics differing chemically substantially from those of the elments to permit separation of the sheath material from the elements when desired;

bundling the sheathed elements in substantially parallel relationship;

mechanically working the bundled sheathed elements in at least one working step to reduce the crosssection of the elements to a preselected filament cross-section of less than approximately 10 microns maximum transverse dimension while concurrently twisting the elements to provide a permanent twist therein and to cause the sheath material to form a matrix extending substantially continuously in cross-section thereby to preclude separation of individual sheathed laments; and

substantially completely removing the sheathing material while maintaining the filaments in twisted bundled relationship to provide a tow of substantially bare separate filaments.

8. The method of forming a tow of substantially bare filaments comprising the steps of:

sheathing each of a plurality of elongated elements from which the filaments are to be formed with a tubular sheath formed of a material having characteristics differing chemically substantially from those of lthe elements to permit separation of the sheath material from the elements when desired;

bundling the sheathed elements in substantially parallel relationship;

mechanically working the bundled sheathed elements in at least one working step to reduce the cross-section of the elements to a preselected filament crosssection of less than approximately l0 microns maximum transverse dimension while concurrently twisting the elements to provide a twist therein and to cause the sheath material to form a matrix extending substantially continuously in cross-section thereby to preclude separation of individual sheathed filaments;

setting the twist in the elements; and

substantially completely removing the sheathing material while maintaining the filaments in twisted bundled relationship to provide a tow of substantially bare separate filaments. 9. The method of forming a tow of substantially bare filaments comprising the steps of:

sheathing each of a plurality of elongated elements from which the filaments are to be formed with a tubular sheath formed of a material having characteristics differing chemically substantially from those of the elements to permit separation of the sheath material from the elements when desired;

bundling the sheathed elements in substantially parallel relationship; mechanically working the bundled sheathed elements in at least one working step to reduce the cross-section of the elements to a preselected filament crosssection of less than approximately l0 microns maximum transverse dimension while maintaining substantially all of the elements continuous in length of at least approximately 50 feet and to cause the sheath material to form a matrix extending substantially continuously in cross-section thereby to preclude separation of individual sheathed filaments; and

substantially completely removing the sheathing material while maintaining the filaments in bundled relationship to provide a tow of substantially bare separate filaments.

10. The method of claim 1 wherein said filaments are formed essentially of said drawable metal.

11. The method of claim 1 wherein said elongated elements are formed of stainless steel and said sheaths are formed of low carbon steel.

12. The method of claim 1 wherein said elongated elements and sheaths are formed of substantially similarly drawable metals and said working comprises drawing the bundled sheathed elements.

13. The method of claim 1 wherein said elongated elements are formed of type 304 stainless steel and said sheaths are formed of loW carbon steel.

14. The method of claim 2 including a plurality of steps of said bundling of a plurality of drawn bundles in parallel relationship and drawing of the bundle of bundles.

15. The method of claim 2 wherein the bundle in each of the bundling steps is in a close packed hexagonal array.

16. The method of claim 2 wherein said elongated elements are formed of drawable metal and said nal crosssection `is less than approximately .0005 inch maximum transverse dimension.

17. The method of claim 7 wherein said elongated elements are formed of drawable metal.

10 19. The method of claim 9 wherein said elongated elements are formed of drawable metal.

References Cited by the Examiner UNITED STATES PATENTS 2,050,298 8/1936 Everett 29-423 X 2,077,682 4/1937 Everett 29-419 3,029,496 5/1962 Levi 29-11555 3,131,469 5/1964 Glaze 29-155.5 3,218,693 11/1965 Allen et al 29l55.5

JOHN F. CAMPBELL, Primary Examiner'.

WHITMORE A. WILTZ, Examiner.

18. The method of claim 8 wherein said elongated ele- 15 P M COHEN, ASSI-Smm Exammm ments are formed of drawable metal. 

1. THE METHOD OF FORMING A TOW OF SUBSTANTIALLY BARE FILAMENTS COMPRISING THE STEPS OF: SHEATHING EACH OF A PLURALITY OF ELONGATED DRAWABLE METAL ELEMENTS FROM WHICH THE FILAMENTS ARE TO BE FORMED WITH A TUBULAR SHEATH FORMED OF A MATERIAL HAVING CHARACTERISTICS PERMITTING THE SHEATHS TO BE PRESSED TOGETHER TO FORM A SUBSTANTIALLY MONOLITHIC BODY AND DIFFERING CHEMICALLY SUBSTANTIALLY FROM THOSE OF THE ELEMENTS TO PERMIT SEPARATION OF THE SHEATH MATERIAL FROM ELEMENTS WHEN DESIRED; BUNDLING THE SHEATHED ELEMENTS IN SUBSTANTIALLY PARALLEL RELATIONSHIP; MECHANICALLY WORKING THE BUNDLED SHEATHED ELEMENTS IN AT LEAST ONE WORKING STEP TO REDUCE THE CROSS-SECTION OF THE ELEMENTS TO A PRESELECTED FILAMENTS CROSSSECTION OF LESS THAN APPROXIMATELY 10 MICRONS MAXIMUM TRANSVERSE DIMENSION AND TO CAUSE THE SHEATH MATERIAL TO FORM A MATRIX EXTENDING SUBSTANTIALLY CONTINUOUSLY IN CROSS-SECTION THEREBY TO PRECLUDE SEPARATION OF INDIVIDUAL SHEATHED FILAMENTS; AND SUBSTANTIALLY COMPLETELY REMOVING THE SHEATHING MATERIAL WHILE MAINTAINING THE FILAMENTS IN BUNDLED RELATIONSHIP TO PROVIDE A TOW OF SUBSTANTIALLY BARE SEPARATE FILAMENTS. 